This invention relates to laser dyes and to the preparation of such dyes. More particularly, this invention relates to a dye of the substituted quinoline class having a rigidized heterocyclic nitrogen atom.
Although a relatively recent advance, the use of liquid organic laser media has been the subject of widespread research. Research has been stimulated by a number of advantages inherent in the use of laser dyes. They generally are capable of laser emission over a wide range of wavelengths, and, using optical techniques, may be tuned to certain specific wavelengths. Compared to gaseous and solid laser media, the dyes are more economical, and do not suffer from cracks or other optical imperfections. Also, a wide range of different organic dyes are available.
Among the first class of compounds found to be efficient laser dyes were the coumarins. See, for example, Schimitshek et al., Optics communications, Vol. II, p. 352 (1974); Reynolds et al., Optics Communications, Vol. 13, p. 222 (1975). It is known that substituents affect important characteristics of the dyes, such as emission spectrum, yield efficiency, and threshold of excitation. Experimentation with various substituents led to the exploration of quinoline derivatives as a class of dyes. For instance, Drexhage in U.S. Pat. No. 3,873,940 reports that a rigidized heterocyclic nitrogen ring produces a more efficient laser emission. Schimitshek et al., supra, report that the addition of a triflouro-methyl group improves the stability of the dye, which to date has been a major problem, in that the optical excitation used to generate laser emissions tends to break down the active components of the molecule, a process termed "bleaching."